2 Answers
2

A terminal is the end of a line. So,
back in the day when the computer was
a mainframe serving many user
accounts, what you'd be sitting at
with your keyboard and display would
be a terminal.

A terminal emulator is when you're
using a computer (a turing machine) to
provide the function of a terminal in
software. This usage would typically
come up because the computer would be
'imitating' a particular type of
terminal in order to communicate with
the mainframe.

A very popular terminal is/was the
VT100. So if I telnet right now to the
server of the local freenet (if they
still exist) I'd be using VT100
emulation.